Expandable spinal stabilization device

ABSTRACT

The present invention relates to an expandable spinal stabilization device that may be inserted into the space between two vertebrae, normally occupied by a disc, in order to stabilize the spine during and after spinal fusion procedures. The invention also relates to a method for using the device. The device generally includes a stack of plates connected by a connecting rod in a manner that allows the plates to adopt a helical configuration about the connecting rod when the plates are rotated about the longitudinal axis of the rod.

FIELD OF THE INVENTION

The present invention relates generally to a surgical apparatus forspinal column fusions.

BACKGROUND

It is commonly estimated that about 80% of Americans will see a healthcare professional at some point in their lives for back problems. Whilemany of these problems can be corrected by exercise and othernon-invasive procedures, sometimes surgery is the proscribed correctivemeasure. A spinal fusion may be the most appropriate treatment forpatients suffering from injuries to spinal vertebrae, protrusion anddegeneration of the cushioning disc between vertebrae (sometimes calledslipped disc or herniated disc), abnormal curvatures (such as scoliosisor kyphosis), and a weak or unstable spine caused by infection or tumor.Spinal fusion has become a common method of correcting spinal problemswith about 285,000 spinal fusions performed in 2001.

The spinal column is comprised of twenty six interlocking vertebraeseparated by discs. Many times it is the motion between the vertebraethat is the source of the problem or severe pain in the patient. Spinalfusion involves the “welding” of two or more these vertebrae into asingle fused bone to limit that motion. After removal of the discmaterial, the welding is normally done by placing a spacer between thevertebrae and then grafting a bone segment to the vertebrae. The bonefor the graft is either taken from elsewhere in the patient (autogenous)or from a bone bank usually consisting of cadaver bone (allograft).Immediate internal bracing, external bracing, and/or casting is thenused to support the region until full healing can take place.

SUMMARY OF THE INVENTION

The present invention describes an expandable spinal stabilizationdevice and a method for using such a device for spinal stabilization andfusion procedures.

The device, comprised of a stack of plates attached to a connecting rod,is designed to be inserted between two vertebrae of a spinal column.Prior to and during insertion the device has a minimal radius associatedwith it, this termed the aligned configuration. The device may then beexpanded by turning the plates in the stack about the longitudinal axisof the connecting rod to produce a helical configuration of the plates,the helical configuration having an effective radius greater than thatof the radius of the aligned configuration.

Many variations relating to the size and shape of the plates in thedevice are contemplated. The plate shape, as viewed from a facialorientation can be any of a multitude of shapes including, but notlimited to circular, oval, square, star-shaped, triangular, or othermulti-sided geometries. The plates may incorporate sharp circumferentialedges to provide a way of gripping onto the bone or promoting bonegrowth, and integrated passages or voids to allow bone growth throughoutthe device. The device should be constructed of a bio-compatiblematerial.

Another aspect of the invention relates to the incorporation of catchesand abutments on the plates to facilitate the formation and retention ofthe helical configuration. The catches may be either raised from theface of a plate or recessed into the surface of the plates.

Another aspect of the invention relates to a tool for turning the stackof plates into a helical configuration. This aspect utilizes a pair ofnested turning sleeves to connect to both the connecting rod of thestack and the top plate of the stack. The inner and/or outer sleeve maybe turned to cause the plates to form a helical configuration about thelongitudinal axis of the connecting rod.

The invention also is directed to methods for stabilizing and/or fusinga spinal column using the device by insertion of the device, in thealigned configuration, between two vertebrae. The device may be insertedinto the intervertebral space using a posterior or posterial lateralapproach, posterior to the transverse process. Once in place, the platesof the device may be turned such that the plates adopt the helicalconfiguration. When the device is used to fuse a spine, bonegrowth-promoting material may be inserted into the intervertebral spacearound the expandable spinal stabilizing device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an Expandable Spinal Stabilization Device with the stack ofplates in the aligned configuration.

FIG. 2 shows an Expandable Spinal Stabilization Device with the stack ofplates in the fully-expanded helical configuration.

FIG. 3 shows a side view of an Expandable Spinal Stabilization Devicewith the stack of plates in the aligned configuration.

FIG. 4 shows a cross-sectional, side view of the Expandable SpinalStabilization Device of FIG. 3.

FIG. 5 shows individual plates of the Expandable Spinal StabilizationDevice of FIGS. 3 and 4, including a catch and an abutment.

FIG. 6 shows individual plates having voids for the insertion of bonegrowth-promoting materials.

FIG. 7 shows the stack of plates of FIGS. 3 and 4 removed from theconnecting rod.

FIG. 8 shows an Expandable Spinal Stabilization Device in the alignedconfiguration along with a turning tool.

FIG. 9 shows an Expandable Spinal Stabilization Device in the helicalconfiguration along with a turning tool.

FIG. 10 is a view of the nested turning sleeves of the turning toolshown in FIGS. 8 and 9.

FIG. 11 is a cross-sectional view of the turning tool of FIG. 10.

FIG. 12 is a stepwise representation of (a) the turning sleeves engagingthe device, (b) the turning of the top plate, and (c) the subsequentturning of the remainder of the plates in the stack of plates.

FIG. 13 shows an Expandable Spinal Stabilization Device, in the alignedconfiguration, inserted into the intervertebral space between twovertebrae of a spine.

FIG. 14 shows an Expandable Spinal Stabilization Device, in the helicalconfiguration, inserted into the intervertebral space between twovertebrae of a spine.

FIG. 15 shows multiple Expandable Spinal Stabilization Devices, in thealigned configuration, inserted into the intervertebral space betweentwo vertebrae of a spine.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an expandable spinal stabilizationdevice and a method for using the same. The stabilization deviceincludes a stack of plates joined together by a connecting rod thatconnects all the plates. When the plates are turned around thelongitudinal axis of the connecting rod, catches and abutments onadjacent plates interlock in a manner that forces the plates to adopt ahelical configuration about the longitudinal axis of the rod, not unlikea spiral staircase. Through the process of forming a helicalconfiguration of the stack of plates, the effective radius of the deviceis increased. This allows for insertion of the device between twovertebrae, in the aligned configuration, and then expansion of thedevice to provide the desired separation of the vertebrae.

In preparing a region of the spine for a stabilization and/or fusionprocedure, some or all of the interior contents is located between thevertebrae may be removed and an expandable spinal stabilization deviceis inserted into the resulting intervertebral space. The surgeon may useone or more of the devices to stabilize the spine in the desiredalignment prior to initiating a bone graft that will form the spinalfusion. If dynamic stabilization rather than fusion is desired, thesurgeon may also choose to leave the disc in place and insert the deviceinto the disc itself, followed by expansion into the helicalconfiguration.

When used to stabilize or fuse a spinal column, the devices providedherein may be fully or only partially expanded in an intervertebralspace. That is, in some applications, the stack of plates will haveadopted a helical configuration along the entire length of the stack,while in other applications the stack of plates may have adopted ahelical configuration along only a portion of the length of the stackwith the remainder of the stack remaining in an aligned or substantiallyaligned configuration. For the purposes of this disclosure, the devicesmay be said to have “adopted a helical configuration” when they are ineither a fully or partially expanded configuration.

The extent to which the devices provided herein expand upon going froman aligned configuration to a helical configuration will vary dependingon such factors as the shapes and sizes of the plates and the rod andthe location of the connections between the plates and the rod. In someembodiments, the effective radius of the device increases by at least20% as it is converted from an aligned configuration to a helicalconfiguration. This includes embodiments where the effective radius ofthe device increases by at least 30% and further includes embodimentswhere the effective radius of the device increases by at least 40% as itis converted from an aligned configuration to a helical configuration.However, the invention is not limited to devices that expand to such anextent.

The plates are an integral part of the device. The size and shape of theplates are not their defining characteristics and the shape may vary fordifferent applications or by the preference of the surgeon. However, thesize of the plates should be selected to allow the device to be insertedwithin an intervertebral space, desirably without extendingsubstantially beyond that space. Each plate is characterized by anobverse face (i.e., a face which is turned toward an observer) and anoppositely-facing reverse face. As viewed from the obverse or reversefaces of the plate, the shape may be round, oval, triangular,rectangular, star-shaped, or may have any of a multitude of othermulti-sided shapes or geometries that are appropriate for the particularsituation. The plates may have sharp circumferential edges, such asblade edges or saw-edges, adapted to decorticate the vertebra as thedevice is inserted or expanded. The saw-edged shape may be defined asone simulating any of a number of common saw blades commonly used bywood craftsmen in circular or table saws. The sharp,circumferential-edged shape may be defined as having sharp points likethe saw-edged shape, a beveled edge like a knife, or a combinationthereof. Some of the shapes may be more advantageous in certainsituations than others. For example, when a larger effective radius ofthe device is needed, the oval shape may be more appropriate than theround, or if decortication of the bone is desired to promote bone growthfor a fusion, then plates having saw-shaped, or a sharp circumferentialedges may be most appropriate. The plates may also have voids, orpassages so that when bone growth begins during the fusion process, thenew bone may infiltrate the device completely and permanentlyincorporate it into the spinal column.

The helical configuration is also an integral part of the presentinvention. The helical configuration may be reminiscent of a screw inshape. The helical shape is adopted by the plates when catches andabutments on adjacent plates engage each other in response to therotation of the plates about the longitudinal axis of the connectingrod. The abutments and catches may be aligned with, positioned on,and/or connected to the plates in any manner that allows the abutmentsand catches on neighboring plates to engage when the connecting rod isrotated about its longitudinal axis. Generally, the abutments andcatches will be aligned with, positioned on, and/or connected to thereverse and obverse faces of neighboring plates such that they extendaway from the face of the plate and toward the space between the plates.

The plates may be connected to the connecting rod in any manner thatallows them to adopt a helical configuration. In some embodiments, therod extends through holes in the plates where the holes are offset fromthe geometric centers of the plates. In an alternative embodiment, therod may extend through loops mounted on and extending outwardly from thecircumferential edge of each plate. The catches and abutments aredesirably disposed on the obverse and reverse faces of the plates andmay take on a variety of shapes, sizes, and positions provided they arecapable of engaging one another when the plates are rotated about thelongitudinal axis of the connecting rod. The plates may be rotated byrotating one of the plates (e.g., the top plate) in the stack, therebycausing the other plates to rotate as their respective catches andabutments become engaged. In other embodiments, the connecting rod isrigidly fixed to one plate in the stack (e.g., the bottom plate) and theplates are rotated by rotating the connecting rod and the plate rigidlyattached thereto. In other embodiments, a helical configuration ofplates may be achieved by rotating one plate (e.g., the top plate) inone direction and rotating the connecting rod and a plate attachedthereto (e.g., the bottom plate) in the opposite direction.

In some embodiments of the device, when an abutment engages a catch, itmerely contacts the catch, forcing the plate on which the catch isattached to move in response to the engagement. In other embodiments,the abutment may fit into or even interlock with the catch. Optionallythe catch may include a locking mechanism, such as a snap fit, thatlocks the abutment to the catch when the device is expanded and thehelical configuration of plates adopted, preventing an unwantedcontraction of the device. In some embodiments, the plates may includemore than one catch and/or abutment on their obverse and reverse faces,such that the devices may be expanded from an aligned configuration to ahelical configuration by rotating the plates in one direction and thencollapsed from its helical configuration back into its alignedconfiguration by rotating the plates in the opposite direction. Forexample, a plate may include a forward catch on its obverse (or reverse)face positioned to engage an abutment when the connecting rod in rotatedin the clockwise direction and a rearward catch on the same facepositioned to engage the abutment when the connecting rod is rotated inthe counterclockwise direction.

The device need not be anchored to the bone via screws or other fixationmethods as described, for example, by Gerber et al. in U.S. Pat. No.6,719,794. Instead the device provides support for the vertebrae andoptionally serves as a support for the growth of new bone material untilthe spinal fusion healing process is complete, whereupon it is then partof the spine. The dimensions of the device may be selected such that thecompressive force on the device is sufficient to stabilize the devicebetween vertebra, preventing it from slipping out of place. However, thedevice may optionally include supplemental means of fixation, such aspedicle screws to further secure the device in the intervertebral space.

The device may be constructed from any appropriate, bio-compatiblematerial known to be safe for spinal fusion and grafting procedures. Aplethora of such materials are well known. These include, but are notlimited to, cobalt chrome, titanium and its many alloys, plastics,ceramics, such as zirconium oxide ceramic and aluminum oxide ceramic,and carbon fiber composites, or other composites. The device mayoptionally have a coating to assist with bony ingrowth.

Methods for using the devices provided herein are also provided. Thesemethods include the step of inserting a device into an intervertebralspace in an aligned (or at least partially aligned) configuration androtating the connecting rod about its longitudinal axis until the platesadopt a helical configuration (full or partial). The device may beexpanded until a stabilizing height is achieved. For example, in someembodiments, the device may be expanded until the patient's natural discheight is restored. In some embodiments, the devices provided hereinfuse as well as stabilize the vertebra. In these embodiments, a bonegrowth-promoting material may be packed around the device after it isimplanted in order to facilitate bone growth and fusion. Optionally, theplates in these devices may include pores, channels or other aperturesthat allow bone growth to permeate the device.

Exemplary embodiments of an expandable spinal stabilization device willnow be explained with reference to the figures. This description isprovided in order to assist in the understanding of the invention and isnot intended to limit the scope of the invention to the embodimentsshown in the figures or described below.

Referring now to FIGS. 1-6, in one embodiment, the expandable spinalstabilization device 100 is constructed from a plurality of plates,including a top plate 105, a bottom plate 110, and a variable number ofinterstitial plates 115. FIGS. 1 and 2 show perspective views of thedevice in the aligned and helical configurations, respectively. FIGS. 3and 4 show side and cross-sectional views of the device of FIG. 1. Thevariable number of interstitial plates 115 is dependent upon on thelength of device 100 needed for the particular patient or region of thespine in which the device 100 will be used. The bottom plate 110 isaffixed to the connecting rod 120 so that it cannot move independentlyof rod 120. The stack is constructed by inserting the connecting rod 120through holes 138 (shown in FIG. 5), in the plates that are offset fromthe geometric centers of the plates, but in the same relative locationon each plate. The bottom plate of the stack 110 is unable to moveindependently of the connecting rod 120, while all the other plates 105,115 may freely turn independent of the connecting rod 120.

FIG. 5 shows more detailed views of two of the plates from the device ofFIGS. 1-4. Each plate of the stack has an obverse face and a reverseface and the plates are arranged such that an obverse face of one platelooks at the reverse face of next plate in the stack. In FIG. 5, theupper plate is shown with its obverse face 131 facing upwardly and thelower plate is shown with its reverse face 133 facing upwardly so theviewer can better see both faces. Of course, the obverse face of the topplate and the reverse face of the bottom plate do not have facing,adjacent reverse and obverse faces. In the illustrative embodiment shownin the figures and as best seen in FIGS. 3-7, the obverse face of eachplate in the stack, except the top plate, features a catch 135, whilethe reverse face of each plate in the stack, except the bottom plate andthe plate immediately adjacent to the bottom plate, features an abutment140. As shown here, the catch may take the form of a slot running alongthe obverse face of the plate in a direction substantially tangentialwith respect to the connecting rod. The abutment takes the form of apost extending downwardly from the reverse face of its plate. Thecatches and abutments are positioned on the faces of the plates suchthat the catch of one plate will engage (e.g., contact or interlockwith) the abutment on the adjacent plate, when the stack is rotated.Thus, when the top plate of the stack is turned about the longitudinalaxis of the connecting rod, the abutment on the reverse face of the topplate contacts the catch on the obverse face of the second plate. Theabutment on the reverse face of the second plate then contacts the catchon the obverse face of the third plate. This series may be continueduntil all catches and abutments have been engaged and the stack achievesa helical configuration.

It should be understood that although the abutments in the embodimentdepicted in the figures are disposed on the reverse faces of the platesand the catches are disposed on the obverse faces, alternativeconstructions are possible. For example, the abutments may be disposedon the obverse faces and the catches on the reverse faces. In otherembodiments, some plates may have abutments on both faces or catches onboth faces, provided that at least one abutment and at least one catchis disposed between adjacent pairs of plates in the stack.

FIG. 6 depicts a variation of the plates of FIG. 5 where the platesinclude a channel 145 into which a bone-growth promoting material may bedeposited and through which the vertebra may develop a fusion.

FIG. 7 shows a perspective view of the device with the top 105 andinterstitial 115 plates removed from the connecting rod 120.

As shown in FIGS. 8, 9, and 12, the top plate 105 may be turned, orrotated, using a turning tool 149. The turning tool, shown in FIGS. 10and 11 includes an outer sleeve 155 having one end 156 that is adaptedto engage a sleeve connector 125 on the obverse face of the top plate105. As shown in the figure, the sleeve connector 125 may take the formof a nut and the end 156 of the outer sleeve 155 may define an openingshaped to fit over and engage the nut. A retaining member (e.g., aretaining ring) 130 may be placed over the sleeve connector 125 to holdthe stack of plates in place on the connecting rod 120. The turning tool149 also includes an inner sleeve 150 nested within outer sleeve 155.The inner sleeve 150 has one end 151 adapted to engage the end of theconnecting rod 120 extending beyond the top plate 105. As shown in thefigures, the end of the connecting rod 120 extending upwardly beyond thetop plate 105 of the stack may be threaded and the end 151 of the innersleeve may define a threaded bore adapted to engage the threaded end ofthe connecting rod 120. Both sleeves may optionally include handles 160,165. The outer sleeve 155 may be turned to produce a helicalconfiguration of plates along the stack. This action is pictoriallysummarized in FIGS. 12 a-12 c.

Another embodiment of the invention is directed at a method for usingthe device 100 in a spine. As depicted in FIGS. 13-15, the device 100 isinserted into the disc region 170 located between vertebra 180 in aspinal column in an aligned configuration (FIG. 13). The turning tool149 is then used to expand the device 100 into the desired helicalconfiguration (FIG. 14), after which the turning tool may be removed.Multiple devices 100 may be used to stabilize both sides of the spine orto stabilize both posterior (rear) and anterior (frontal) sides of thespine (FIG. 15). As shown in FIGS. 13-15, the devices may be insertedinto an intervertebral space using a posterior or posterial lateralapproach, posterior to the transverse process. However, otherapproaches, such as an anterior approach, may also be used. Optionally,a tube or cannula may be used to protect surrounding tissue during theinsertion of the device.

A plethora of variations on the general theme of the above embodimentsare contemplated, such as the ordering of the catches and abutments onthe obverse and reverse faces of the plates of the stack. Therefore, inanother embodiment, arrangements of catches and abutments may bedescribed in the more generic manner that follows. Each plate of thestack has an obverse face and a reverse face and the plates are arrangedsuch that an obverse face of one plate looks at the reverse face of nextplate in the stack. Each face of a plate in the stack features either acatch or an abutment with the catches and abutments arranged on theobverse and reverse faces of the plates in a manner such that for eachcatch there is an abutment on the adjacent face of the next plate in thestack. The ordering of the catches and abutments is immaterial as longas for every catch there is an abutment on the adjacent face of the nextplate in the stack. Thus, one plate may have two catches as long as thetwo adjacent faces to that plate have abutments that may be contacted bythe catches. In FIGS. 2-6, the catches are depicted as slots 135, raisedfrom the face of the plates 110, 115. However, it is also apparent thatthe slots may be recessed into the plates to provide the same function.The abutments are depicted as posts 140 and are shown on the reverseface of the plates 105, 115, while the slots are shown on the obverseface of plates 110, 115. However, it is also apparent that the posts mayreside on the obverse face of plates 110, 115, while the slots are onthe reverse face of plates 105, 115. While it is not an object of thisinvention to recite all the combinations of catches and abutments, it iscontemplated that those features may be arranged on the plates in anymanner such that any given structure, catch or abutment, has thecomplementary structure on the adjacent facing plate.

FIG. 6 details the use of other voids or passages 145 in the plates as aregion through which bone growth may occur. Other contemplatedembodiments would have the plates constructed from very porous,bio-compatible substances that would allow bone growth throughout theplate structure allowing for fusion of the spinal column.

It should be understood that various changes and modifications to theembodiments described herein would be apparent to those skilled in theart. Such changes and modifications can be made without departing fromthe spirit and scope of the present invention. It is, therefore,intended that such changes and modifications be covered by the appendedclaims.

1. An expandable spinal stabilization device comprising: a. a pluralityof plates arranged in a stack; and b. a connecting rod connecting theplurality of plates; wherein the plates are connected to the connectingrod such that the plurality of plates adopt a helical configurationabout the longitudinal axis of the connecting rod when the plates areturned about the longitudinal axis of the connecting rod; and furtherwherein the dimensions of the device render it suitable for insertioninto an intervertebral space.
 2. The device according to claim 1 whereinthe plurality of plates comprise a top plate, a bottom plate, and one ormore interstitial plates disposed between the top plate and bottomplate, each plate comprising an obverse face and a reverse face, furtherwherein the connecting rod extends through the obverse and reverse facesof the top plate and the interstitial plates at a position offset fromthe geometric center of the plates.
 3. The device according to claim 1wherein the plates are circular.
 4. The device according to claim 1wherein the plates are oval.
 5. The device according to claim 1 whereinthe circumferential edges of the plates are multi-sided.
 6. The deviceaccording to claim 5 wherein the plates are square.
 7. The deviceaccording to claim 5 wherein the plates are star-shaped.
 8. The deviceaccording to claim 5 wherein the plates are triangular.
 9. The deviceaccording to claim 1 wherein the circumferential edges of the platesprovide sharp cutting edges.
 10. The device according to claim 9 whereinthe plates are saw-shaped.
 11. The device according to claim 1 whereinthe plates and the connecting rod are comprised of a biocompatiblematerial.
 12. The device according to claim 1 wherein the plates haveintegrated passages.
 13. The device according to claim 1 comprising atop plate, a bottom plate, and one or more interstitial plates disposedbetween the top plate and the bottom plate, each plate comprising anobverse face and a reverse face such that a pair of adjacent facescomprising the obverse face of one plate and the reverse face of anadjacent plate is provided for each pair of adjacent plates in thestack, wherein: a. one face in at least one pair of adjacent facescomprises a catch; b. the other face in the at least one pair ofadjacent faces comprises an abutment; and further wherein c. everyabutment is positioned in a manner to engage the catch of an adjacentface when the plates are rotated about the longitudinal axis of theconnecting rod.
 14. The device according to claim 13 wherein one face inevery pair of adjacent faces except the final pair comprises a catch andthe other face in every pair of adjacent faces except the final paircomprises an abutment.
 15. The device according to claim 13 wherein oneface of each pair of adjacent faces comprises a catch and the other faceof each pair of adjacent faces comprises an abutment.
 16. The deviceaccording to claim 13 wherein the reverse face of each pair of adjacentfaces comprises an abutment and the obverse face of the at least onepair of adjacent faces comprises a catch.
 17. The device according toclaim 13 wherein each catch comprises a slot running along the obverseor reverse face of a plate in a direction substantially tangential withrespect to the circumference of the connecting rod and each abutmentcomprises a post extending away from the obverse or reverse face of aplate.
 18. The device according to claim 17 wherein the slots are raisedfrom the obverse or reverse faces of the plates.
 19. The deviceaccording to claim 17 wherein the slots are recessed in the obverse orreverse faces of the plates.
 20. The device according to claim 13wherein the bottom plate is unable to move independently of theconnecting rod and the top plate and interstitial plates are connectedto the connecting rod in a manner that allows them to rotate about thelongitudinal axis of the connecting rod.
 21. The device according toclaim 20 wherein the obverse face of the top plate comprises a sleeveconnector disposed thereon and the connecting rod comprises an endextending beyond the obverse face of the top plate, the device furthercomprising a turning tool, the turning tool comprising: a. an outersleeve having an end adapted to engage the sleeve connector; and b. aninner sleeve nested within the outer sleeve, the inner sleeve having anend adapted to engage the end of the connecting rod extending beyond thetop plate such that when the inner sleeve engages the connecting rod andthe outer sleeve engages the sleeve connector, the helical configurationis achieved by turning at least one of the inner and outer sleeves. 22.The device according to claim 21 wherein the sleeve connector is a nutand the end of the outer sleeve is adapted to engage the nut, andfurther wherein the end of the connecting rod extending beyond the topplate is threaded and the end of the inner sleeve is adapted to engagethe threads.
 23. A method of stabilizing a spinal column, the methodcomprising inserting the expandable spinal stabilization deviceaccording to claim 1 into an intervertebral space in the spinal columnand turning the plates about the longitudinal axis of the connecting roduntil the plurality of plates adopt a helical configuration.
 24. Themethod according to claim 23 further comprising inserting a bonegrowth-promoting material in the intervertebral space around theexpandable spinal stabilizing device.
 25. The method according to claim23 wherein the device is inserted using a posterior or posterial lateralapproach.
 26. The method according to claim 25 wherein the device isinserted with the aid of a tube or cannula.
 27. The method according toclaim 23 wherein the device is inserted using an anterior approach.